英文:
Why has methods are not generated using protoc 3.17.* if in protobuf repo they say it should?
问题
阅读这里：https://github.com/protocolbuffers/protobuf/blob/master/docs/field_presence.md#go-example 中的Golang示例：
m := GetProto()if (m.HasFoo()) {// Clear the field:m.Foo = nil} else {// Field is not present, so set it.m.Foo = proto.Int32(1);}
如果我使用：
protoc pkg/user.proto --go_out=. --go_opt=module=my_app --go-grpc_out=. --go-grpc_opt=module=my_app
和：
syntax = "proto3";package example;message MyPlayer {uint64 id = 1;optional string description = 2;uint32 qty = 3;optional uint64 age = 4;}
它不会生成任何has<T>()方法。
为什么？
// Code generated by protoc-gen-go. DO NOT EDIT.// versions:// protoc-gen-go v1.26.0// protoc v3.17.3
如果我使用生成的MyPlayer proto字段而不是方法，我错了吗？
例如：
if MyPlayer.description != nil {description = *MyPlayer.description}
而不是
description = MyPlayer.GetDescription()
这不是我想要的（我想要检测nil值）。
英文:
Reading here: https://github.com/protocolbuffers/protobuf/blob/master/docs/field_presence.md#go-example the Golang example:
m := GetProto()if (m.HasFoo()) {// Clear the field:m.Foo = nil} else {// Field is not present, so set it.m.Foo = proto.Int32(1);}
if I use:
protoc pkg/user.proto --go_out=. --go_opt=module=my_app --go-grpc_out=. --go-grpc_opt=module=my_app
with:
syntax = "proto3";package example;message MyPlayer {uint64 id = 1;optional string description = 2;uint32 qty = 3;optional uint64 age = 4;}
it doesn't generate any has<T>() method.
Why?
// Code generated by protoc-gen-go. DO NOT EDIT.// versions:// protoc-gen-go v1.26.0// protoc v3.17.3
Am I wrong if I use MyPlayer generated proto fields instead of methods?
Example:
if MyPlayer.description != nil {description = *MyPlayer.description}
instead of
description = MyPlayer.GetDescription()
which is not what I want (I want to detect nil values).
答案1
得分: 3
这份文档是错误的，如此处所述：https://github.com/golang/protobuf/issues/1336：
https://github.com/protocolbuffers/protobuf/blob/master/docs/field_presence.md#go-example 上的文档是错误的。在 proto3 中使用 "optional" 会生成与 proto2 中相同的字段。
那份文档是错误的。生成的代码中没有
Has方法。通过将字段与nil进行比较来测试是否存在。
正确重写这些示例：
// 字段 foo 没有存在性。// 如果字段 foo 不为 0，则将其设置为 0。// 如果字段 foo 为 0，则将其设置为 1。m := GetProto()if m.Foo != 0 {// “清除”字段：m.Foo = 0} else {// 默认值：字段可能不存在。m.Foo = 1}
// 字段 foo 有存在性。// 如果 foo 已设置，则清除它。// 如果 foo 未设置，则将其设置为 1。m := GetProto()if m.Foo != nil {// 清除字段：m.Foo = nil} else {// 字段不存在，因此设置它。m.Foo = proto.Int32(1)}
修复该文档的 PR：
protocolbuffers/protobuf#8788
英文:
That docs is wrong, as reported here: https://github.com/golang/protobuf/issues/1336:
> The documentation on https://github.com/protocolbuffers/protobuf/blob/master/docs/field_presence.md#go-example is incorrect. Using "optional" in proto3 makes the field be generated just as it would in proto2.
> That doc is wrong. There are no Has methods in the generated code. Test for presence by comparing fields to nil.
>
> Rewriting those examples correctly:
>
>
> // Field foo does not have presence.
> // If field foo is not 0, set it to 0.
> // If field foo is 0, set it to 1.
> m := GetProto()
> if m.Foo != 0 {
> // "Clear" the field:
> m.Foo = 0
> } else {
> // Default value: field may not have been present.
> m.Foo = 1
> }
>
>
>
> // Field foo has presence.
> // If foo is set, clear it.
> // If foo is not set, set it to 1.
> m := GetProto()
> if m.Foo != nil {
> // Clear the field:
> m.Foo = nil
> } else {
> // Field is not present, so set it.
> m.Foo = proto.Int32(1)
> }
>
> PR to fix that doc:
> protocolbuffers/protobuf#8788
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